The French inquiry will involve the public department for environment and health protection as well as the Anti-Corruption Office of the Judicial Police.

Volkswagon's former CEO, Martin Winterkorn, has already come under investigation by the German state attorney, after it received complaints from people who had raised the issue anonymously. Prosecutors said yesterday that he was no longer under official investigation.

The German probe is seeking to clarify whether criminal or civil charges will be brought over the emissions issue, specifically whether it may constitute fraud and to determine who knew about it.

Winterkorn resigned last Wednesday while repeatedly denying any knowledge of the software.